1. Field of the Invention
The present invention relates to image reading devices used for reading out image data in a light-transparent portion of a target to be light-irradiated such as banknotes.
2. Description of the Related Art
As such conventional image reading device, for example, a device has been disclosed in FIG. 1 of Japanese Patent Application Publication Laid-Open No. 2000-113269 (referred to as Patent Document 1). That is, in Patent document 1, a banknote identification apparatus is disclosed in which light is incident on a watermarked image of a banknote, etc., the light that has passed therethrough is detected by an artificial retina chip, information on the image shape, etc. of the transparent portion (hereinafter also referred to as watermarked portion) and on whether the image is present or not therein is processed by a knowledge processing circuit, and thus the banknote, etc. is authenticated.
An image reading device is disclosed in FIG. 2 of Japanese Patent Application Publication Laid-Open No. 2003-87564 (referred to as Patent Document 2), in which both transmission-type and reflection-type image readers are used. The image reading device disclosed is configured in such a way that a light source for a transparent document is installed in a document cover, a document mat is attachably and detachably engaged to the document cover, and thus when a light-reflective document is read, the document mat is attached to the document cover, while, when a transparent document is read, the document mat is detached from the document cover.
An illumination device and an image reading device using the same are disclosed in FIG. 8 of Japanese Utility Model Application Laid-Open No. 1995-7259 (referred to as Patent Document 3), in which light incident inside a transparent rod 21 through one of end faces 21a and 21b thereof is repeatedly total-reflected by outer peripheral surfaces of the transparent rod 21, and, while traveling toward the other end face 21a or 21b, the light is scattered by a light diffusion face 31 formed on one of the outer peripheral surfaces and exits from a face 21c opposite to the face 31, whereby a uniform illuminance level can be obtained in the main-scanning direction X.
An image reading device is disclosed in FIG. 1 of Japanese Patent Application Publication Laid-Open No. 2007-194797 (referred to as Patent Document 4), in which image data in a transparent portion of a target to be light-irradiated can be read out by disposing light sources on one side of the target, tilted at a predetermined angle with respect to a plane perpendicular to the target, and receiving light emitted from the light sources and scattered by the roughness of the transparent portion of the target.
In the banknote identification apparatus disclosed in Patent Document 1, when the identification is performed with respect to the watermarked portion of the banknote, etc., after so-called direct light from the light source has been transmitted through the watermarked portion of the banknote, etc., the transmitted light is converted into electrical signals, and thus the image in the watermarked portion of the banknote, etc. is read out.
The image reading device disclosed in Patent Document 2 can also be considered that so-called a transmission-type image reading device (hereinafter, also referred simply to as “transmission-type device”) and a reflection-type image reading device (hereinafter, also referred simply to as “reflection-type device”) are combined; however, also in this system, when the image in the light transparent portion is read out by the transmission-type device, the reading is performed by using so-called direct light.
In the image reading device disclosed in Patent Document 3, because, by arranging a relatively small number of LEDs in a sub-scanning direction, light emitted therefrom is guided in a main-scanning direction, and gradually emitted from the light diffusion face so that its distribution becomes uniform, the illuminance is insufficient so that the device cannot be suitably used for high-speed reading such as reading when a document moving in high speed, which has been a problem.
Moreover, the image reading device disclosed in Patent Document 4 is configured in such a way that, by using horn-shaped light guides 22 for guiding light emitted from transmission-type light sources 21, light emitted at a predetermined angle from light exit portion 22a of the horn-shaped light guides 22 is incident on a portion 5, to be light irradiated, along a conveying path of a document 1; therefore, a problem has occurred that, because its light-guide path between the transmission-type light sources 21 to the light-irradiation portion 5 is relatively long, and its size in a direction perpendicular to the conveying direction of transmission-type light-source assembly 20 is large, the device is unsuitable to be miniaturized, and irradiation can only be performed with a single predetermined angle.